The Fred Jones vs. Demetris Nichols roster-spot battle keeps tilting toward Jones, who played 20 smooth minutes in Monday’s preseason opening night win in South Carolina. And now you can add another SG to the mix on Friday when, according to what Isiah Thomas said at practice today, Allan Houston is expected to launch his comeback with his first Knick practice. (Can you say longshot?)

Nichols didn’t come in until the fourth quarter, playing 9:58, making two ghastly turnovers. He’s obviously a little shaky right now, realizing he is behind in the race. On one turnover, Nichols rose for a jumper and in midair, tried to pass the ball tothe sidelines where no Knick was within 10 feet. The ball sailed out of bounds. No question, Nichols is a better shooter than Jones. But Jones is more poised and passes the ball well. He’s one of the few NBA players who still makes good use of the bounce pass.

Obviously, defense is Jones’ strength and the chief reason they want to keep him. I hear Nichols was ticked off at The Post’s story last weekend in which his defense was questioned.

“I know I can play defense,” Nichols told me. “That’s not the problem.”

The problem, according to Nichols’ agent Bill Neff, is contracts. Jones has a guaranteed pact and they don’t want to eat it. Jones’ contract also is expiring, making it trade bait.

“It’s not about defense, it’s about contracts,” Neff told me over the phone the othe day.

I wrote in the paper today Isiah would like to keep Jones for support in the locker room. Jones was one of Isiah’s guys in the Pacers’ locker room. Coaches need as many allies as possible, especially with Thomas’ longterm status potentially on shaky ground.

Jones told me, “I’m indebted to him. He drafted me. It was his pick and a lot of people doubted him. He stuck out his neck for me and I just want to prove him right.”

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Tickets are still available for tomorrow night’s preseason home opener vs. Maccabi Tel Aviv and there’s no Yankee game to watch as an excuse not to go. Proceeds for tickets sales are going to an Israeli children’s charity, Migdal Ohr.